Multi-pole circuit breaker with adjustable thermal trip unit

ABSTRACT

A multi-pole circuit breaker with adjustable thermal trip unit characterized by a circuit breaker mechanism having a plurality of pole units, means releasable when released from a latched position to effect simultaneous opening of the circuit breaker contacts, a multi-pole trip device including trip means for each of said pole units, each of said trip means being constructed to operate upon the occurrence of certain current conditions to effect release of said releasable means, and each pole unit comprising a bimetal element responsive to current flow to effect heating thereof. The circuit breaker also comprises a first trip bar and a second trip bar, the first trip bar being mounted to oscillate between latched and unlatched positions and being biased in the latched position, the second trip bar being pivotally mounted on the first trip bar at spaced locations between the ends of the first trip bar and being pivotally adjustable to varying spacings from the bimetal elements, and an adjusting cam mounted on the first trip bar and engageable with the second trip bar for adjusting the second trip bar with respect to the bimetal elements.

CROSS REFERENCE TO RELATED APPLICATION

This invention is related to that disclosed in the application of AlbertR. Cellerini and Louise N. Ricci, Ser. No. 551,937, filed Feb. 21, 1975.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to circuit breakers and, moreparticularly, to circuit breakers having adjustable thermal trip means.

2. Description of the Prior Art

The conventional thermal tripping mechanism of a circuit breaker is wellknown in the art and consists mainly of a movable trip bar which carriesa releasable latch. As shown in U.S. Pat. No. 3,211,860, the trip bar isactuated by adjacent bimetal strips which respond to temperaturegenerated by the current flowing through the circuit breaker. Adifficulty with some circuit breakers of the type shown in that patent,is the problem of precisely resetting an adjusting screw of one pole tocorrespond with settings of corresponding screws for the other poles inthe circuit breaker so that all screws are engaged by a correspondingbimetal element for the same current rating.

SUMMARY OF THE INVENTION

It has been found that in accordance with this invention, that theforegoing problem may be overcome by providing a multi-pole circuitbreaker comprising a circuit breaker mechanism having a plurality ofpole units, each pole unit comprising a pair of contacts, meansreleasable when released from a latched position to effect simultaneousopening of all of said pairs of contacts, a multi-pole trip devicecomprising trip means for each of said pole units, each of said tripmeans being constructed to operate upon the occurrence of certaincurrent conditions to effect release of said releasable means, such poleunit comprising a bimetal element responsive to current flow to effectheating thereof, trip bar means movable to unlatch the releasable meansand being biased in the latched position, the trip bar means comprisinga first trip bar and a second trip bar, the first trip bar being mountedto oscillate between latched and unlatched positions, the second tripbar being pivotally mounted at spaced locations between the ends of andon said first trip bar and being pivotally adjustable to varyingspacings from the bimetal elements, and adjustment means comprising acam on the first trip bar and engageable with the second trip bar formoving the second trip bar with respect to the bimetal elements.

The advantage of the device of this invention is that the thermal ratingcan be varied from 100 to 70% by turning the adjusting cam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a circuit breaker shown in theopen position;

FIG. 2 is an enlarged plan view of the removable trip device of thebreaker shown in FIG. 1;

FIG. 3 is a front view with most of the cover broken away of the tripdevice;

FIG. 4 is an enlarged sectional view taken on the lines IV--IV of FIG.3;

FIG. 5 is an enlarged view of the first and second trip bars;

FIG. 6 is an end view of the trip bars as shown in FIG. 5; and

FIG. 7 is a plan view of a portion of the trip bars.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the circuit breaker shown therein is of the three-pole typeand comprises generally a base 11 and a removable cover 13, both ofwhich may be molded from suitable electrically insulating material.Inasmuch as a detailed description of the circuit breaker is set forthin U.S. Pat. No. 3,211,860, the description of the circuit breakerportion is limited to the parts that are essential to the operation ofthe invention disclosed herein.

Each of the three-poles is provided with terminals at opposite ends ofthe base 11 indicated generally at 15 and 17. The circuit breakerincludes a stationary contact 21, a movable contact 23, and an arcextinguisher indicated generally at 25, for each pole unit. A commonoperating mechanism generally indicated at 27 is provided forsimultaneously actuating the three movable contacts to open and closedpositions. A trip device generally indicated at 29 automatically opensthe contacts 21, 23 in response to predetermined overload conditions ina circuit through any pole unit of the breaker.

The terminal 15 is disposed at the outer end of a conducting strip 31that extends into the housing and rigidly supports the stationarycontact 21. The movable contact 23 for each pole unit is mounted on arigid contact arm 33 which is supported on a switch arm 35 secured to atie bar 37 which extends across all of the pole units and supports allof the switch arms 35 for unitary movement to the open and closedpositions. The contact arm 33 is connected by means of a flexibleconductor 39 to an intermediate or trip unit thermal member or conductor41 which is secured at one end thereof to the base 11 by a screw 42. Theconducting member 41 extends through the trip unit 29 and is connectedat its outer end to the terminal structure 17. Accordingly, a circuitthrough the circuit breaker extends from the terminal 17 through theconductors 41, 39, the contact arm 33, the contacts 21, 23, theconductor 31 to the terminal 15.

The operating mechanism 27 comprises a pivoted operating lever 45, apair of toggle links 47, 49, overcenter spring means 51, and a pivotedreleasable cradle or arm 53 which is controlled by the trip device 29.An integral handle 55 extends through an opening 57 in the cover 13 toenable manual operation of the breaker between OFF and ON positions.

As shown in FIGS. 2, 3 and 4, the trip device is contained within anelectrically insulating housing comprising a base or support member 71and a cooperating cover 73. The trip device 29 is similar to that setforth in U.S. Pat. No. 3,211,860, for which reason an abbreviateddescription is set forth herein. Similar electro-responsive trippingmeans, generally indicated at 75, are provided for each of the threepole units and function separately in response to any current overloadcarried by the corresponding conductor 41. A bimetallic element orbimetal 77 has one end secured by means of rivets 78 to one leg of thelooped portion (FIG. 4) of the conductor 41. The other free end of eachbimetal 77 is disposed adjacent an adjusting screw 79.

As shown in FIGS. 2 and 4, the trip device 29 also comprises a latchingmechanism 81 disposed on the exterior side of the base 71. The latchingmechanism comprises a pair of stationary mounting arms 83, a latch lever85, and a trip lever 87. The latch lever 85 is pivotally mounted on thelatching mechanism 81 and (FIG. 1) retains the cradle 53 in the latchedposition. The trip lever 87 retains the latch lever 85 in the unlatchedposition, as shown in FIGS. 1, 2 and 4, due to engagement of the triplever with a trip member 89. The mounting arms 83 are secured to amounting frame 91 and extend through an opening 93 in the base 71 intothe interior of the trip compartment enclosed by the base 71 and thecover 73.

In accordance with this invention, the trip device 29 comprises a firsttrip bar 95 and a second trip bar or trip arm 97. As shown in FIG. 5,the trip bar 95 includes a pair of spaced openings 99. The inner endportions of the mounting arm 83 extend into the openings 99 and the tripbar 95 is mounted on mounting pins 101 which extend into the openingsfrom the trip bar 95. Thus, the trip bar is pivotally mounted in placefor movement between tripped and untripped positions. The trip arm 97 ispivotally mounted on the trip bar 95 by means of metal brackets 103 atintermediate locations on the bar 95 and arm 97. More particularly, thebrackets 103 are suitably secured such as by rivets 105 on the trip arm97 and comprise outturned portions 107 that extend into the openings 99where they are mounted on pins 101 which extend in opposite directionsfrom the ends of the trip bar. Thus, the trip arm 97 is rotatablymounted on the trip bar 95.

Rotation of the trip arm 97 with respect to the trip bar 95 isinfluenced by biasing means, such as a coil spring 109, the upper endsof which are secured to the trip arm 97 and the lower ends of which aresecured to the trip bar 95. The springs 109 retain the trip arm 97 inthe desired position above the trip bar 95 as shown in FIG. 6.

In addition to the springs 109 the trip arm 97 is subject tomanipulation by adjustment means for rotating it through an angle α(FIG. 6). The adjustment means may comprise any one of a variety ofmovable members mounted on either the trip bar 95 or the trip arm 97 andextending over the surface of the other bar or arm for adjusting theangular movement of the arm with respect to the bar. The preferredadjusting means (FIGS. 5, 6 and 7) comprises a cam structure generallyindicated at 111. The cam structure 111 comprises a rotatable eccentricshaft 113 that is mounted on a mounting pin 117 which is embedded in thetrip bar 95. The cam structure 111 is rotated by inserting an implement,such as a screwdriver, into a slot 115 at the upper end of the shaft 113so as to vary the angle α between the trip bar 95 and the trip arm 97 byrotating the shaft (FIG. 7) toward or away from the surface of the triparm which is retailed against the cam by the spring 109.

As shown in FIG. 6, the lower end of the shaft 113 includes a projection117 which limits the degree of rotation of the shaft by engaging a stoppin 119 that is seated in the bar 95. Thus, the cam travel is limited tothe maximum and minimum of the eccentric differential of the cam surfacewith the true center of the shaft, or 180°.

In accordance with this invention, the several calibrating screws 79 aremounted on the trip arm 97. When the trip device 29 is originallyassembled the three calibrating screws 79 are set for each correspondingbimetal element 77 (FIG. 4). Thereafter, to vary or change the thermalrating, it is merely necessary to turn the shaft 113 in order to changethe distances between the three calibrating screws 79 and thecorresponding bimetal elements 77.

Accordingly, the thermal rating of a multi-pole circuit breaker can bevaried from 70% to 100% merely by turning one adjusting member.

What is claimed is:
 1. A multi-pole circuit breaker comprising a circuitbreaker mechanism having a plurality of pole units, each pole unitcomprising a pair of contacts, means releasable when released from alatched position to effect simultaneous opening of all of said pairs ofcontacts, a multi-pole trip device comprising trip means for each ofsaid pole units, each of said trip means being constructed to operateupon the occurrence of certain current conditions to effect release ofsaid releasable means, each pole unit comprising a bimetal elementresponsive to current flow to effect heating thereof, trip bar meansmovable to unlatch the latch lever and being biased in the latchedposition, the trip bar means comprising a first trip bar and a secondtrip bar, the first trip bar being mounted to oscillate between latchedand unlatched positions, the second trip bar being pivotally mounted onand at spaced locations between the ends of the first trip bar and beingpivotally adjustable to simultaneously vary the spacings from thebimetal elements, and adjustment means on one of the first and secondtrip bars for adjusting the second trip bar with respect to the bi-metalelements.
 2. The circuit breaker of claim 1 in which the adjustmentmeans comprises a movable member mounted on one of the first and secondtrip bars for adjusting the angular position of the other trip bar withrespect to said one trip bar.
 3. The circuit breaker of claim 2 in whichthe movable member is mounted on the first trip bar and comprises anenlarged portion that is movable toward and away from the second tripbar to effect changes in the spacing between the second trip bar and thebimetal elements.
 4. The circuit breaker of claim 1 in which theadjustment means comprises an adjusting cam.
 5. The circuit breaker ofclaim 4 in which the cam comprises an elongated shaft and an eccentricsurface.
 6. The circuit breaker of claim 5 in which the elongated shaftis rotatably mounted on the first trip bar and the eccentric surfacecontacting the second trip bar.